Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Stock Option Activity Narrative (Details)

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Stockholders' Equity - Stock Option Activity Narrative (Details) - USD ($)
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares) 1,359,000 1,000,000 3,800,000
Share-based compensation arrangement by share-based payment award, options, exercises in period, intrinsic value $ 12,200,000 $ 1,500,000 $ 0
Exercise of options tax benefit 2,200,000 300,000  
Unrecognized share-based compensation expense, options 17,800,000    
2015 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares)     3,200,000
2021 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares)     600,000
Share-based compensation expense 19,000,000    
General, administrative and marketing | 2021 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense 17,100,000    
Other operating | 2021 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 1,900,000    
Time vesting stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares)     3,300,000
Performance vesting stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares)     500,000
Stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Contractual term 10 years   10 years
Vesting period 4 years   4 years
Lock-up period     180 days
Share-based compensation expense $ 11,800,000 19,800,000 $ 320,500,000
Unrecognized share-based compensation expense, period of recognition 2 years 7 months 6 days    
Stock options | Center operations      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 500,000 1,400,000 12,700,000
Stock options | General, administrative and marketing      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense 11,000,000 17,800,000 303,300,000
Stock options | Other operating      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 300,000 $ 500,000 $ 4,500,000